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Electronic properties of the (001) surface of cubic BaZrO3 with BaO and ZrO2 terminations have been studied using first-principles calculations. Surface structure, partial density of states, band structure and surface energy have been obtained. We find that the largest relaxation appears in the first layer of atoms, and the relaxation of the BaO-terminated surface is larger than that of the ZrO2-terminated surface. The surface rumpling of the BaO-terminated surface is also larger than that of the ZrO2-terminated surface. Results of surface energy calculations reveal that the BaZrO3 surface is likely to be more stable than the PbZrO3 surface.

We have performed first principles calculations of Fe-doped BaTiO3 and SrTiO3. Dopant formation energy, structure distortion, band structure and density of states have been computed. The dopant formation energy is found to be 6.8 eV and 6.5 eV for Fe-doped BaTiO3 and SrTiO3 respectively. The distances between Fe impurity and its nearest O atoms and between Fe atom and Ba or Sr atoms are smaller than those of the corresponding undoped bulk systems. The Fe defect energy band is obtained, which mainly originates from Fe 3d electrons. The band gap is still an indirect one after Fe doping for both BaTiO3 and SrTiO3, but the gap changes from Γ–R point to Γ–X point.

Full-potential linearized augmented plane wave method and Boltzmann transport properties have been used to investigate the crystal structure and electronic structure of Mg2Si. Electronic conductivity, Seebeck coefficient and power factor are calculated. Energy band structure shows that Mg2Si is an indirect semiconductor with energy band gap of about 020 eV. Transport properties versus the doping level have been calculated for the n type and p type doped materials at 700 K. The optimal carrier concentration corresponding to the maxima of power factor are obtained, which are 7749×1019 cm-3 and 1346×1020 cm-3 for the p-doping and n-doping respectively. Maximum ZT value of 093 has been estimated in combination with experimental data of thermal conductivity. From the transport properties at different temperatures, we found that the ratio of power factor to relaxation time is enhanced when the temperature increases. Optimum doping level of materials used in middle and high temperature range is higher than that of materials used in low temperature.

The possibility of forming cascading energy levels in SrTiO3 by doping Bi and Cu as an example is analyzed by using the density-functional-theory based first principles calculations of the electronic structure. The results show that both Bi doping and Cu doping can introduce a defect level in the forbidden band，and Co-doping of Bi and Cu can introduce two defect levels in the forbidden band. Electrons at the top of valence band can transit to the bottom of conduction band through a cascade transition process. Using the nonradiative transition model，we point out that the probability of electronic transition from the valence band to the conduction band through a cascade transition is much higher than that of direct transition from the valence band to the conduction band. The cascade transitions can effectively increase the carrier concentration in the conduction band.